Synaptic acetylcholinesterase (ColQ-AChE) is localized at the neuromuscular junctions in skeletal muscle. It is a hetero-oligomeric protein formed from 12 catalytic subunits (AChE) and 3 non-catalytic subunits (ColQ). How the expression of this enzyme is regulated remains obscure. I present here new evidence that the non- catalytic ColQ subunit regulates expression of the catalytic AChE subunit by rescuing this subunit from degradation, and that ColQ-AChE levels are regulated postranscriptionally by muscle activity. Our preliminary studies also show that an inhibitor of protein disulfide isomerase (PDI), an ER chaperone, inhibits the synthesis of all AChE forms in muscle cells. I propose that muscle activity regulates synaptic AChE posttranslationally at the level of ColQ folding in part by regulating the rate of ColQ-AChE assembly. To test this hypothesis, we will study the effect of PDI over-expression and knockdown on AChE expression in muscle cells. We will also identify which ColQ AChE subunits are substrates of PDI and will determine whether muscle activity regulates PDI expression and how that correlates with ColQ-AChE levels. Finally, we will determine where in the cells the ColQ and AChE subunits are initially attached and whether complex oligomerization occurs subsequently. [unreadable] [unreadable] [unreadable]